Throughout the twentieth century, the prior art has developed for various types of aircraft. In general, the aircraft can be divided into two basic types of aircraft. The first type of aircraft is commonly referred to as a fixed wing aircraft whereas the second type of aircraft is commonly referred to as a rotary wing aircraft.
In fixed wing aircraft, an engine may transmit output to a horizontally extending shaft for rotating a propeller to provide the horizontal thrust to the fixed wing aircraft. In the alternative, the engine may be a jet engine providing horizontal thrust to the fixed wing aircraft by the discharge of hot gases.
A traditional fixed wing airplane must have a forward center of mass. If it did not, and the airplane wings entered a stalled condition, there would be no means of lowering the nose of the aircraft to regain flying speed and therefore the aircraft would be inherently unstable. The design physics for airplanes require a center of mass forward of the center of lift acting in a fulcrum arrangement to provide inherent flight stability so long as the aircraft is in flight mode. This fulcrum arrangement provides downward pressure from the tail of the aircraft in flight which counterbalances the static forward center of mass. A fixed wing aircraft is inherently unstable below the stall speed of the particular aircraft. The fixed wing aircraft utilizes displaceable flight surfaces, the aircraft reacting to forces generated from the airflow over the control surfaces during forward flight to achieve control of the aircraft. Flaps, elevators, rudders, ailerons, and stabilators are all examples of these types of flight controls.
In a rotary wing aircraft, the rotary wing aircraft includes an engine having a vertically extending shaft for rotating a rotor to provide a vertical thrust to the rotary wing aircraft. As the rotor rotates about the vertically extending shaft, the rotor provides a vertical lift to the rotary wing aircraft. The rotary wing aircraft must have a pendulum center of mass. The rotary wing aircraft is stable at zero forward airspeed because the center of mass of the aircraft is suspended as a pendulum below the center of lift of the rotating rotor. The rotary wing aircraft relies on vectored thrust instead of flight controls to achieve control of the aircraft. Collective pitch, differential rotor blade thrust, and cyclic pitch are all examples of these types of vectored thrust flight controls. Elevators, ailerons are not utilized. The rotary wing pilot is able to alter the thrust of the rotor longitudinally, laterally, and vertically, to determine the flight path desired.
Each of the rotary wing aircraft and the fixed wing aircraft has certain advantages and disadvantages. The rotary wing aircraft has the advantage of vertical takeoff and landing and hovering maneuvers due to the vertical thrust from a rotating rotor. Compared with a fixed wing aircraft, the rotary wing aircraft has the disadvantage of inefficient cross country travel, the inability for high speed horizontal flight, and lower operational altitudes.
Compared with the rotary wing aircraft, the fixed wing aircraft has the advantage of being able to travel more efficiently at high speeds and fly at high altitudes. The fixed wing aircraft has the disadvantage of substantial takeoff and landing speed thus requiring a substantial runway space for takeoff and landings. In addition, the fixed wing aircraft is incapable of flight below operating airspeeds or hovering maneuvers due to the loss of lift over the fixed wing of the aircraft due to insufficient speed.
Those attempts which have tried to create a heliplane, or some similar conversion of a helicopter into an airplane by attaching a wing to the vehicle, have been quite unsuccessful. The spinning rotor creates enormous drag at high forward speeds, and one still has all the problems with the forward and rearward sweeping rotor blades and the problem that the center of mass remains inherently different from an airplane.
Examples of known “heliplanes” are U.S. Pat. Nos. 3,934,843, 4,730,795, 6,086,016, 5,758,844, and 6,343,768, which are incorporated by reference herein in their entireties.
All of the previous art has failed to address the fundamental difference in the center of mass, both dynamic and static, between existing vertical flight aircraft (helicopters) and existing horizontal flight aircraft (airplanes).
All of the previous art has failed to address the fundamental difference in efficiency between the forward movement of vertical flight aircraft (helicopters) and the forward movement of existing horizontal flight aircraft (airplanes).
Conversely, all of the previous art has failed to address the fundamental difference in efficiency between the vertical movement of vertical flight aircraft (helicopters) and the vertical movement of existing horizontal flight aircraft (airplanes).
Although many of the United States patents referenced in this application, and other patents of which I am aware, have attempted to provide a hybrid aircraft that has the advantages of a fixed wing aircraft and a rotary wing aircraft, the aforementioned United States patents fail to accomplish this task. None has been a commercial success. One fundamental reason why the hybrid aircrafts of prior art have failed to accomplish this task is due to a period of instability encountered during the period of transition between the operation as a fixed wing aircraft and the operation as a rotary wing aircraft. During this period of transition, the center of mass of the hybrid aircraft moves between the operation as a rotary wing aircraft and the operation as a fixed wing aircraft, and vice versa. The movement of the center of mass of the hybrid aircraft creates a fundamental instability in the operation of the hybrid aircraft making the hybrid aircraft difficult to control during this transition period. This will be best explained with reference to FIGS. 1 and 2.
FIG. 1 is a side view of a conventional rotary wing aircraft 10R comprising a fuselage 12R and an engine 14R. The engine 14R is coupled through a vertical shaft 20R for rotating a rotor 30R to provide vertical lift to the rotary wing aircraft 10R. A tail section 50R is rigidly secured to the fuselage 12R having a tail rotor 56R. The tail rotor 56R has the same function as the rudder 56F in the conventional fixed wing aircraft 10F of FIG. 2.
The rotor 30R of the rotary wing aircraft 10R provides a center of lift (CL) for rotary wing aircraft 10R. The center of mass (CM) is underslung as a pendulum below of the center of lift (CL) of the rotary wing aircraft 10R. Since the rotor 30R provides a center of lift (CL) directly above the center of mass (CM) of the rotary wing aircraft 10R, the rotary wing aircraft 10R can operate as a gravity stabilized pendulum in a hovering mode with zero horizontal speed. Control of the rotary wing aircraft is obtained by vectoring the thrust of the rotor. When the thrust produced by rotor 30R is vectored in a rearward direction, a component of the once vertical thrust of the rotating rotor 30R then provides a horizontal thrust component to propel the rotary wing aircraft 10R in a forward direction, opposite to the vectored thrust.
As the thrust produced by the rotor 30R is angled further in the rearward direction to induce forward motion, the component of the rotating rotor 30R providing lift for the rotary wing aircraft 10R decreases in accordance with the cosine of the angle of said thrust in the rearward direction. This is a fundamental limitation of a rotary wing aircraft 10R.
FIG. 2 is a side view of a conventional fixed wing aircraft 10F comprising a fuselage 12F and an engine 14F. The engine 14F is coupled through a horizontal shaft 20F for rotating a propeller 30F to provide forward motion to the fixed wing aircraft 10F. The fixed wing aircraft 10F includes a fixed wing 40F rigidly secured to the fuselage 12F of the fixed wing aircraft 10F. Typically, the fixed wing 40F includes plural ailerons 42F and plural flaps 44F. A tail section 50F is rigidly secured to the fuselage 12F and has a horizontal stabilizer 54F and a vertical stabilizer 52F. The horizontal stabilizer 54F includes plural elevators 58F whereas the vertical stabilizer 52F includes a rudder 56F.
The fixed wing 40F of the fixed wing aircraft 10F provides a center of lift (CL) for fixed wing aircraft 10F. The center of mass (CM) of the fixed wing aircraft 10F is located forward of the center of lift (CL) of fixed wing aircraft 10F. The center of mass (CM) being located forward of the center of lift (CL), i.e., a forward center of mass, is necessary to achieve dynamic stability in flight and is required to regain control of the fixed wing aircraft 10F in the event of a stall condition.
A stall condition exists when the angle of attack of the fixed wing of aircraft 10F exceeds the critical angle needed to maintain airflow to the upper surface of the wing. The airflow then separates from the upper surface of the wing, thereby destroying lift and control of the aircraft. Since the fixed wing aircraft 10F has a forward center of mass, the loss of lift in the stall condition lowers the angle of attack of the wing, thus reestablishing attached airflow over the fixed wing 40F to provide adequate lift to support the fixed wing aircraft 10F. The reestablishment of the lift of the fixed wing 40F enables a pilot to regain control of the fixed wing aircraft 10F. Although the fixed wing aircraft 10F has been shown as a single engine propeller driven fixed wing aircraft 10F, it should be understood that the same principle of operation applies to a jet aircraft and multi-engine variants of both types.
As discussed above, many in the prior art of which I am aware have attempted to create a hybrid aircraft that combines the benefits of the rotary wing aircraft 10R and the fixed wing aircraft 10F. Unfortunately, the hybrid aircraft of such prior art could not solve the problem of the fundamental difference in the position of the center of mass (CM) between the rotary wing aircraft 10R and the fixed wing aircraft 10F. During vertical takeoff, if the aircraft is to be fundamentally stable, then all hybrid aircraft must be operated as the rotary wing aircraft 10R with the center of mass (CM) being located as a pendulum below the center of lift (CL) of the hybrid aircraft. However, during horizontal flight, if the hybrid aircraft is to be operated as a fixed wing aircraft and be inherently stable, then, the center of mass (CM) must be located forward of the center of lift (CL) of the hybrid aircraft. In such a hybrid, the movement of the center of mass (CM) of the hybrid aircraft creates a period of instability during the transition of the hybrid aircraft from the operation as the rotary wing aircraft 10R to the operation as the fixed wing aircraft 10F.